Prussian blue, a blue pigment used for paints and fabrics was the first synthetic coordination compound. It has a cubic structure with $\mathrm{Fe}$ in both $+2$ and $+3$oxidation states. It is obtained by the addition of iron(III) salts to sodium/potassium ferrocyanide in aqueous solution. The action of sodium ferrocyanide with sodium nitrite in aqueous solution produces a beautiful ruby red diamagnetic iron complex $\left(\mathrm{X}\right)$, which gives a violet colored complex $\left(\mathrm{Y}\right)$ in the presence of sulphide. $\mathrm{X}$ on treatment with $\mathrm{NaOH}$ gives back sodium ferrocyanide. The correct statement(s) is/are